The invention is applicable to any security system using an optical cable, such as a system for transmitting confidential information by means of optical fibers or an optical cable system able to seal a container.
This type of sealing system is described in the document EP-A-0147328, known subsequently as "document I", and in the document U.S. Pat. No. 4,688,891, reference to be made to these documents later in this text.
The users of a security system using an optical cable are able to detect any intrusion or attempted intrusion into this system.
The system described in the document I is intended to detect any break-in or attempted break-in in order to steal all or part of the contents of the container sealed by this system.
In order to do this, images, respectively taken immediately after sealing of the container and during a subsequent inspection, are compared with an image transmitted by the optical fibers of the cable comprising the system when these fibers receive a luminous beam.
If the images differ, it is assumed that there has been an infraction or attempted infraction between the time when the container has been sealed and the time of inspection.
However, considerable progress achieved in the field of the butt welding of optical fibers is rendered ineffective as, by using the light transmitted by the cable fibers, it becomes extremely difficult to detect this intrusion or attempted intrusion, which is almost completely concealed.